Simulating Solar Neighborhood Brown Dwarfs I: The Luminosity Function Above and Below the Galactic Plane

Brown dwarfs form the key, yet poorly understood, link between stellar and planetary astrophysics. These objects offer unique tests of Galactic structure, but observational limitations have inhibited the large-scale analysis of these objects to date. Major upcoming sky surveys will reveal unprecedented numbers of brown dwarfs, among even greater numbers of stellar objects, enabling the statistical study of brown dwarfs. To extract the comparatively rare brown dwarfs from these massive datasets, we must understand how they will look in upcoming surveys. In this work, we construct a synthetic population of brown dwarfs in the Solar Neighborhood to explore their evolutionary properties using Gaia-derived star formation histories alongside observational mass, metallicity, and age relationships. We apply the cloudless Sonora Bobcat, hybrid SM08, and gravity-dependent hybrid Sonora Diamondback evolutionary models to the sample. We present the simulated luminosity function and its evolution with distance from the Galactic Plane. Our simulation shows that brown dwarf population statistics are a function of height above/below the Galactic Plane and sample different age distributions. Interpreting the local sample requires combining evolutionary models, the initial mass function, the star formation history, and kinematic heating. Our models are a guide to how well height-dependent samples can test these scenarios. Sub-populations of brown dwarfs farther from the Plane are older and occupy a different region of brown dwarf parameter space than younger sub-populations closer to the Galactic Plane. Therefore, fully exploring population statistics both near and far from the Plane is critical to prepare for upcoming surveys.